Taste and colours...
The positive is you can adjust this already excellent sounding amp
Regarding the values and relative levels betwen harmonic, you really need to find out what YOU prefer.
I played quite a bit with that and you may want to look into the H2 and B1 Korg thread to see how much impact all this can have on the sound.
IMHO, very personal:
- it all depends on the overall leel of harmonics in your existing system, from source to LS, so one can give a general rule on one component and the summ matters
- you may want to determine what YOU like, taste matters at a given level
- IMHO you want indeed low levels of harmonic but up to a certain point
- Yes, IMHO you want to play with some levels of H2 and H3, you don't really want the others
- I found some level of H2 very interesting, although less than H2 lovers in my case, but quite a significant level, and also "negative H2" very interesting re soundstage... whatever H2 I like the fluidity and body it seems to give and some other bits... experience yourself
- I prefer less H3 than H2 but some H3 is also good to my ears re dynamic and punch, some rawness perhaps
Oh, and all these are quite audible and enjoyable, but still subtle somewhere... you won't turn a bad set up to a good one adding H2... nor will you suffer from anything bad or degrade your excellent amp keeping things as intented or as they are, what ever the current harmonic profile you may have. I see it as fine tuning, but quite audible again...
All very subjective and all with another device as I don't even own a USSA-5 (but have all main parts for the FSSA-2 I hope to start whenever I can shamelessly follow someone more competent than me
Enjoy music either way
Claude
The positive is you can adjust this already excellent sounding amp
Regarding the values and relative levels betwen harmonic, you really need to find out what YOU prefer.
I played quite a bit with that and you may want to look into the H2 and B1 Korg thread to see how much impact all this can have on the sound.
IMHO, very personal:
- it all depends on the overall leel of harmonics in your existing system, from source to LS, so one can give a general rule on one component and the summ matters
- you may want to determine what YOU like, taste matters at a given level
- IMHO you want indeed low levels of harmonic but up to a certain point
- Yes, IMHO you want to play with some levels of H2 and H3, you don't really want the others
- I found some level of H2 very interesting, although less than H2 lovers in my case, but quite a significant level, and also "negative H2" very interesting re soundstage... whatever H2 I like the fluidity and body it seems to give and some other bits... experience yourself
- I prefer less H3 than H2 but some H3 is also good to my ears re dynamic and punch, some rawness perhaps
Oh, and all these are quite audible and enjoyable, but still subtle somewhere... you won't turn a bad set up to a good one adding H2... nor will you suffer from anything bad or degrade your excellent amp keeping things as intented or as they are, what ever the current harmonic profile you may have. I see it as fine tuning, but quite audible again...
All very subjective and all with another device as I don't even own a USSA-5 (but have all main parts for the FSSA-2 I hope to start whenever I can shamelessly follow someone more competent than me
Enjoy music either way
Claude
Just a quick update (and note to myself): if I bias the output at 1 A and set P3 and P4 for 28.0 mV (standard values in Fabs build guide), I get pretty much the same profile of harmonics as that shown by Fab (1 W into 8 Ohm). Upping the output bias current requires some imbalance in the P3 and P4 settings to maintain the harmonics profile. For 1.3 A output bias, I found that P3 = 30 mV and P4 = 28 mV gives the profile in the attachment, which is very similar to the 1 A / 28 mV / 28 mV profile, but with slightly lower 3rd harmonic and more output current headroom.
Running at 1.5 A also works out ok. Heat is fine in my workshop, where I have no heating (about 12 °C ambient right now). However, under the normal living-room conditions in my listening room, the amp gets a bit too hot for the cat.
Oh, and I believe I figured out in which camp I am when it comes to H2 vs H3... but the difference is subtle compared to the other goodies you get from the USSA5 sound.
Running at 1.5 A also works out ok. Heat is fine in my workshop, where I have no heating (about 12 °C ambient right now). However, under the normal living-room conditions in my listening room, the amp gets a bit too hot for the cat.
Oh, and I believe I figured out in which camp I am when it comes to H2 vs H3... but the difference is subtle compared to the other goodies you get from the USSA5 sound.
Attachments
This is excellent work Mbrennwa!
Glad you seem to like it You can also report back once you have more break-in done.
Also, a picture of the completed assembly in your good looking chassis could be fun to see.
As for your camp for H2 and H3 it would interesting to get your personal preference...
H3 level reduction with higher bias current is quite normal for a class A design.
Section 19.1.3.1 of the manual gives insights about the effect of different input currents for positive and negative part of circuit. This info was brought up mainly for USSA-5.1 where the use of bjt for driver tends to reduce dissimilarity between positive and negative waveforms thus reducing H2. Since there is some reports of correlation between sound preferences based on H2/H3 ratio I just wanted to give the opportunity to play with it. But as Ggetzoff and yourself indicate this ratio does not provide a night and day difference but subtle one at these levels. What is more important for me is the very low levels of higher harmonics compared to H2 and H3. Personally I believe that the sound character of the amp is not mainly determined by this H2/H3 ratio unless H2 is unusually set very high which can obviously also provide a more prominent coloured sound
Fab
Glad you seem to like it
You can also report back once you have more break-in done.Also, a picture of the completed assembly in your good looking chassis could be fun to see.
As for your camp for H2 and H3 it would interesting to get your personal preference...
H3 level reduction with higher bias current is quite normal for a class A design.
Section 19.1.3.1 of the manual gives insights about the effect of different input currents for positive and negative part of circuit. This info was brought up mainly for USSA-5.1 where the use of bjt for driver tends to reduce dissimilarity between positive and negative waveforms thus reducing H2. Since there is some reports of correlation between sound preferences based on H2/H3 ratio I just wanted to give the opportunity to play with it. But as Ggetzoff and yourself indicate this ratio does not provide a night and day difference but subtle one at these levels. What is more important for me is the very low levels of higher harmonics compared to H2 and H3. Personally I believe that the sound character of the amp is not mainly determined by this H2/H3 ratio unless H2 is unusually set very high which can obviously also provide a more prominent coloured sound
Fab
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I will take some proper photos when I am ready.
The manual says this: "The total of the two current values should remain the same (28+28 = 56mV or 27+29 = 56mV or 29+27=56mV)."
Why is this? I guess the idea might be to keep the "total bias" of the driver / output stage as it is, but I am not sure if there's something else I am missing.
I just played with different P3 and P4 values and then re-adjusted P1 and P2 to get the desired output-stage bias and to zero the DC offset.
I will take some proper photos when I am ready.
The manual says this: "The total of the two current values should remain the same (28+28 = 56mV or 27+29 = 56mV or 29+27=56mV)."
Why is this? I guess the idea might be to keep the "total bias" of the driver / output stage as it is, but I am not sure if there's something else I am missing.
I just played with different P3 and P4 values and then re-adjusted P1 and P2 to get the desired output-stage bias and to zero the DC offset.
Hi Mbrennwa
I could have indicated about the same value (56mv) to get the same overall results. This is the input stage current that is adjusted with P3/P4. Higher input current means lower load resistor value (to keep same bias) but then lower input stage gain, thus lower open loop gain thus lower damping factor....
Lower input current means higher damping factor.....There are many combinations that can be done but please start with the original settings of the manual to get the feel of it so you will get the same amplifier as the other builders...
Fab
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I have now listened for a few hours with the USSA5 in my system. I am not good with describing sound, so I will just say that ggetzoffs post is spot on! The USSA-5 is a much better amplifier than my FirstWatt F5 (built on Nelsons kitchen table), Babelfish Aleph J with power JFET output, or KT66 MacGyver amps. The USSA-5 really is a gem that stands out from the plethora of (good!) amplifiers here on diyAudio and elsewhere!
My system: Raspberry Pi with I2S reclocker --> DDDAC with DAC chips directly connected to a Sowter 9335 TVC for BAL-to-SE conversion and volume control --> USSA-5 --> Open Source Monkey Coffin speakers
My system: Raspberry Pi with I2S reclocker --> DDDAC with DAC chips directly connected to a Sowter 9335 TVC for BAL-to-SE conversion and volume control --> USSA-5 --> Open Source Monkey Coffin speakers
Hi Mbrennwa
Your sound report is like sweet bananas for the monkey’s birthday ...
I am very glad you like it and you appear to also have a nice implementation.
I am also reassured to confirm that Ggetzoff was not in a disturbed mental state when he has written his sound report
What is the final bias used and level of H2 over H3 at 1Wrms that you set it to?
Fab
Your sound report is like sweet bananas for the monkey’s birthday ...
I am very glad you like it and you appear to also have a nice implementation.
I am also reassured to confirm that Ggetzoff was not in a disturbed mental state when he has written his sound report
What is the final bias used and level of H2 over H3 at 1Wrms that you set it to?
Fab
